Now this force is that which is considered as residing in the cerebral membranes and the brain, from which it comes that every movement of a joint, every contraction of the muscles, every spontaneous influence that is exerted upon the individual members, renders our earthen statue active and mobile as though by some mechanism. For the most pure form of heat and the most subtle form of liquid, being united by their respective forces through a process of mixture and combination, nourish and sustain by their moisture the brain, and hence in turn, being rarefied to the most pure condition, the exhalation that proceeds from that organ anoints the membrane which encloses the brain, which, reaching from above downwards like a pipe, extending through the successive vertebrae, is (itself and the marrow which is contained in it) conterminous with the base of the spine, itself giving like a charioteer the impulse and power to all the meeting-points of bones and joints, and to the branches of the muscles, for the motion or rest of the particular parts.
For this cause too it seems to me that it has been granted a more secure defence, being distinguished, in the head, by a double shelter of bones round about, and in the vertebrae of the neck by the bulwarks formed by the projections of the spine as well as by the diversified interlacings of the very form of those vertebrae, by which it is kept in freedom from all harm, enjoying safety by the defence that surrounds it.
So too one might suppose of the heart, that it is itself like some safe house fitted with the most solid defences, fortified by the enclosing walls of the bones round about; for in rear there is the spine, strengthened on either side by the shoulder-blades, and on each flank the enfolding position of the ribs makes that which is in the midst between them difficult to injure; while in front the breastbone and the juncture of the collarbone serve as a defence, that its safety may be guarded at all points from external causes of danger.
As we see in husbandry, when the rain fall from the clouds or the overflow from the river channels causes the land beneath it to be saturated with moisture (let us suppose for our argument a garden, nourishing within its own compass countless varieties of trees, and all the forms of plants that grow from the ground, and whereof we contemplate the figure, quality, and individuality in great variety of detail); then, as these are nourished by the liquid element while they are in one spot, the power which supplies moisture to each individual among them is one in nature; but the individuality of the plants so nourished changes the liquid element into different qualities; for the same substance becomes bitter in wormwood, and is changed into a deadly juice in hemlock, and becomes different in different other plants, in saffron, in balsam, in the poppy: for in one it becomes hot, in another cold, in another it obtains the middle quality: and in laurel and mastic it is scented, and in the fig and the pear it is sweetened, and by passing through the vine it is turned into the grape and into wine; while the juice of the apple, the redness of the rose, the radiance of the lily, the blue of the violet, the purple of the hyacinthine dye, and all that we behold in the earth, arise from one and the same moisture, and are separated into so many varieties in respect of figure and aspect and quality; the same sort of wonder is wrought in the animated soil of our being by Nature, or rather by Nature’s Lord. Bones, cartilages, veins, arteries, nerves, ligatures, flesh, skin, fat, hair, glands, nails, eyes, nostrils, ears—all such things as these, and countless others in addition, while separated from one another by various peculiarities, are nourished by the one form of nourishment in ways proper to their own nature, in the sense that the nourishment, when it is brought into close relation with any of the subjects, is also changed according to that to which it approaches, and becomes adapted and allied to the special nature of the part. For if it should be in the neighbourhood of the eye, it blends with the visual part and is appropriately distributed by the difference of the coats round the eye, among the single parts; or, if it flow to the auditory parts, it is mingled with the auscultatory nature, or if it is in the lip, it becomes lip; and it grows solid in bone, and grows soft in marrow, and is made tense with the sinew, and extended with the surface, and passes into the nails, and is fined down for the growth of the hair, by correspondent exhalations, producing hair that is somewhat curly or wavy if it makes its way through winding passages, while, if the course of the exhalations that go to form the hair lies straight, it renders the hair stiff and straight.
Our argument, however, has wandered far from its purpose, going deep into the works of nature, and endeavouring to describe how and from what materials our particular organs are formed, those, I mean, intended for life and for good life, and any other class which we included with these in our first division.
For our purpose was to show that the seminal cause of our constitution is neither
